Laser appartus

ABSTRACT

A laser apparatus comprises storage means for storing a power source voltage of each pulse at the time of continuous pulse oscillation for one cycle, with each voltage correlated with an identifier which specifies the respective pulse, and output control means for, when a pulse is generated, reading from the storage means the source voltage of a pulse having the same identifier, and performing pulse oscillation on the basis of the source voltage. Thus the influence of the spiking phenomenon during a burst mode operation is eliminated as much as possible, and thereby the accuracy of laser beam machining is still more improved.

TECHNICAL FIELD

The present invention relates to a laser apparatus to output a laserbeam for a machining apparatus to apply prescribed machining, using alaser beam, to semiconductors, polymer materials, or inorganic materialsand particularly to an improvement to attain uniform pulse energy valuescontinuously, when effecting burst mode operation, which is switchingalternately between a continuous oscillation action for continuous pulseoscillation of a laser beam at a prescribed frequency and a stoppingaction for stopping the pulse oscillation for a prescribed time, and animprovement to make uniform the shifting cumulative exposure wheneffecting machining with a step and scan system.

BACKGROUND ART

In the field of microfinishing using ultraviolet light, such as withsemiconductor exposure apparatuses, strict exposure control is necessaryin order to maintain the resolution of the circuit pattern at a constantlevel or better. However, excimer lasers used as the light source insemiconductor exposure apparatuses have variations in the pulse energyof each pulse since these lasers are so-called pulse excitation gasdischarge lasers. It is necessary to reduce these variations in order toimprove the precision of exposure control.

Therefore, a method for decreasing the variation in the cumulative valueof the irradiated energy, by decreasing the light energy output with onepulse oscillation and irradiating the same location to be machined witha plurality of successive pulses, is being considered.

In consideration of production, however, a large number of pulses is notpreferable. Also, in the field of semiconductor exposure, thesensitivity of photosensitive materials applied to wafers has improvedin recent years and exposure with a small number of pulses is becomingpossible. For this reason, a method to increase the number of pulses andreduce variations in total energy of the irradiated light isunavoidable.

However, semiconductor exposure apparatuses repeatedly alternate betweenexposure and stepped movement. Therefore, the operating state of theexcimer laser, the light source, as shown in FIG. 23, necessarilybecomes the burst mode of switching between the action of continuouspulse oscillation to oscillate the laser beam continuously at a fixedfrequency, and the action of stopping the pulse oscillation for aprescribed time. In effect, the burst mode switches alternately betweenthe continuous pulse oscillation period and the oscillation stoppageperiod. In effect, in FIG. 23, one IC chip formed on a semiconductorwafer undergoes machining with a pulse group constituting a singlecontinuous pulse oscillation period. Moreover, FIG. 23 shows the energyintensity of each pulse when the excitation intensity (charging voltage)is set at a constant value.

As discussed above, since the excimer laser is a pulse excitation gasdischarge laser, it is difficult for it to continuously oscillate at apulse energy of a constant size. The cause of this is as follows: thedischarge disturbs the density of the laser gas within the dischargespace, making the next discharge irregular and unstable; because of thisirregular discharge, etc., a localized temperature increase occurs onthe surface of the discharge electrode, deteriorating the nextdischarge; and discharge becomes irregular and unstable.

In particular, that trend is marked in the initial phase of thecontinuous pulse oscillation period; the so-called spiking phenomenonappears as shown in FIGS. 23 and 24. In the spiking phenomenon, acomparatively high pulse energy is attained initially in the spike zone,including the first few pulses after the oscillation stoppage period t,and afterwards pulse energy gradually decreases. When this spike zone isfinished, the pulse energy passes through a plateau zone where a stablevalue at a comparatively high level is maintained, and then enters astable zone (stationary zone).

This type of excimer laser apparatus with a burst mode operation hassuch problems as variations in the energy of each pulse, discussedabove, decreasing the precision of exposure control, and the spikingphenomenon markedly enlarging the variations further and greatlyreducing the precision of exposure control.

Moreover, in recent years, the sensitivity of photosensitive materialsapplied to wafers has increased, as discussed above, making possibleexposure with a small number of continuous pulses; the trend is for areduced number of pulses. However, variations in pulse energy haveaccordingly increased as the number of pulses has decreased. It hasbecome difficult to sustain the precision of exposure control throughonly the multiple pulse exposure control discussed above (control byreducing the amount of energy output in a single pulse oscillation andirradiating the same location to be machined with a plurality ofsuccessive pulses).

Therefore, the present applicant is applying for patents for variousinventions using the property that pulse energy increases as excitationintensity (charging voltage) increases and relating to so-called spikingprevention control, to prevent the initial energy increase due to thespiking phenomenon, by changing the discharge voltage (charging voltage)for each pulse, through reducing the discharge voltage (chargingvoltage) of the initial pulse in continuous pulse oscillation in burstmode and gradually increasing the discharge pulse (charging voltage) ofsubsequent pulses, as shown in FIG. 25 (Japanese Patent Application No.4-191056, Japanese Patent Application Laid-open No. 7-106678 (JapanesePatent Application No. 5-249483), etc.).

Specifically, FIG. 26 shows the energy intensity of each pulse in thecase of excitation intensity (charging voltage) being fixed at aconstant value, as shown in FIG. 23 or 24 noted above. A spikingphenomenon is exhibited wherein a comparatively high pulse energy isattained initially at a constant state of excitation intensity and pulseenergy gradually decreases thereafter.

FIG. 25 shows an excitation intensity pattern in the case of the spikingphenomenon occurring as shown in FIG. 26. The excitation intensitypattern shows the excitation intensity displacement to correct theincreased energy of the initial pulse in the spiking phenomenon andattain a constant pulse energy value. This instance shows the excitationintensity pattern with pulse energy conversion. In other words, becausepulse energy is high for the first few pulses in the spiking phenomenonas shown in FIG. 25, the excitation intensity is reduced for the firstfew pulses in continuous pulse oscillation, and then the excitationintensity is gradually increased. In this way, during pulse oscillation,the source voltage is applied according to this excitation intensitypattern for each pulse oscillation. This prevents the initial rise inpulse energy due to the spiking phenomenon and controls so that thepulse energy of each pulse is the same for all pulses.

This background art has source voltage data to set the energy of eachpulse in continuous pulse oscillation to a desired target value(constant value), in view of various parameters such as the oscillationstoppage time t (See FIG. 23) and power lock voltage (source voltagedetermined according to the deterioration of laser gas), stored inmemory in advance for each pulse in continuous pulse oscillation.Meanwhile, this background art detects the pulse energy duringcontinuous pulse oscillation conducted up to the previous time, comparesthis detected value and the pulse energy target value, and corrects thepreviously stored source voltage data corresponding to each pulse basedon the results of this comparison. This correction is called spikekiller control.

However, this background art gives rise to the following problems; themeasures to prevent the spiking phenomenon are not necessarilysufficient.

The problems are explained using FIG. 27.

FIG. 27 shows the pulse waveform during burst mode operation insemiconductor exposure. In the figure, No. 1, No. 2, . . . No. j, . . .No. N are pulse groups. Each pulse group is constituted of a prescribednumber of continuous pulses as shown in FIGS. 23, 24, and 26. A shortlaser oscillation stoppage time ΔTj appears between No. j and No. j+1. Along laser oscillation stoppage time ΔT appears after the No. N pulsegroup.

This type of arrangement of pulse groups derives from semiconductorexposure being conducted while the process alternates between exposureof the chip on the wafer and movement of the optical system.Specifically, the action of exposing one particular chip on a wafer isconducted with the No. j pulse group and the action of exposing the nextchip is conducted with the No. j+1 pulse group. The time necessary forexposure and movement the optical system is ΔTj. The exposure of asingle wafer is entirely finished at the time when the switching betweenthis exposure and movement of the optical system and the oscillation ofthe series of pulse groups from No. 1 to No. N is completed. Here, ΔT isthe time in which the exposed wafer is transported out and the nextwafer is transported into the exposure apparatus and aligned in aposition where exposure is possible. After this ΔT, the series of pulsegroups No. 1', No. 2', . . . No. j', . . . No. N', which is the same asNo. 1 to No. N, continues.

In the case of the laser operation discussed above, the excitationintensity pattern of the No. 1 pulse group, which is directly precededby the same laser oscillation stoppage time (ΔT in this case), is usedin the oscillation of the next No. 1' pulse group after ΔT following thecompletion of No. N, in order to suppress the spiking phenomenonoccurring in each pulse group. Also, the excitation intensity pattern ofthe No. N pulse group, which is directly preceded by the same laseroscillation stoppage time, is used for the No. 2' to No. N' pulse groups(ΔT to ΔTN-1 is the same length of time). In other words, the data forthe previous pulse group No. 1 is used for the initial pulse group No.1' since the influence of the spiking phenomenon is marked, but becausethe influence of the spiking phenomenon gradually decreases, the No. Npulse group data is used for the pulse groups No. 2' and later forsimple control.

The influence of the spiking phenomenon in each pulse group issuppressed to a certain extent. However, the experiments of the presentinventors show that the variations in pulse energy are not necessarilyresolved due to the cause discussed below and the effect of thesuppression is not stable.

The cause is that the spiking phenomenon is influenced by the hysteresisof prior pulse oscillation. In other words, the spiking phenomenon hasthe property of becoming more marked when the laser oscillation stoppagetime in burst mode is greater. Therefore, the following phenomenonoccurs: the suppression of the spiking phenomenon easily becomesinsufficient in the first half, No. 1', No. 2'. . . , of the series ofpulse groups No. 1' to No. N' following No. 1 to No. N in FIG. 27, andthe effects of suppressing the spiking phenomenon are sufficientlydisplayed in the second half of the pulse groups, . . . No. N'-2, No.N'-1, No. N'. In this way, the excitation intensity pattern of a pulsegroup is different depending on where the pulse group falls within theseries of pulse groups. The suppression of the spiking phenomenon doesnot take effect even with the application of data for a pulse groupdirectly preceded by the same laser oscillation stoppage time.

Consequently, because pulse oscillation is controlled using thepreceding excitation intensity pattern, variations in pulse energy arenot resolved with a conventional laser apparatus as represented in theJapanese Patent Application No. 4-191056 and suppression of the spikingphenomenon is still desirable.

Also, with the background art, the suppression of variations in pulseenergy is insufficient in zones other than the spike zone, since spikekiller control is performed in the plateau zone and stable zone as wellas in the spike zone shown in FIG. 24. Moreover, the suppression ofpulse energy is insufficient even when spike killer control is performedonly in the spike zone and plateau zone.

This is thought to be due to the following: the influence of the laseroscillation stoppage (laser is stabilized) remains strong in the initialperiod of continuous pulse and the output power becomes high compared toother zones even if the same source voltage is impressed; and in thesubsequent plateau zone and stable zone, the influence of laseroscillation stoppage decreases, while the influence of pulse oscillation(increased electrode temperature, turbulence of laser gas, etc.) is evenstronger.

Also, with the background art, the amount of data stored to effect spikekiller control for all pulses in continuous pulse oscillation becomesgreat. This gives rise to the following problems: a large memorycapacity and time to read data from memory are required.

However, as memory capacity is increased, the exposure system forapparatuses for exposing semiconductors will change from a steppersystem, for stopping the stage and effecting exposure, to a step andscan system, for effecting exposure while moving the stage. Theadvantage of this step and scan system is that large areas can beexposed. For example, when using a lens with a field size of 36 mm, theexposed area is a 25 mm square in the stepper system, but the step andscan system makes possible the exposure of a large area of 30×40 mm. Inthe future, chip sizes will increase as the degree of integrationincreases and high precision exposure with the step and scan system willbe desired.

In other words, with the step and scan system, machining is effectedwhile zones irradiated by pulse laser beams on a machined item arestaggered at a prescribed pitch each time a pulse laser is radiated, sothat a prescribed number NO of pulse lasers, each established inadvance, irradiate all points on the machined item. In this step andscan system, however, it is difficult to effect control in such a mannerthat the exposure of each point on a machined item is the same becausethe pulse laser beam is scanned continuously. Therefore, an effectivecontrol method is desirable.

It is an object of the present invention to provide a laser apparatus,being a laser apparatus operated in the burst mode, wherein theinfluence of the spiking phenomenon is eliminated as much as possible,so as to further improve the precision of machining with a laser beam.

Also, it is an object of the present invention to provide a laserapparatus which can make uniform the exposure of each point on amachined item in the case of effecting machining with the step and scansystem.

DISCLOSURE OF THE INVENTION

The present invention provides a laser apparatus which effects a burstmode operation having as one cycle an operation of switching at aprescribed frequency between a continuous oscillation action forcontinuous pulse oscillation of a laser beam at a prescribed frequencyand a stoppage action for stopping the pulse oscillation for aprescribed time, and controls a source voltage in such a manner that anenergy output in the pulse oscillation reaches a prescribed magnitude,characterized in that the apparatus comprises:

storage means for storing the source voltage of each pulse wheneffecting the continuous pulse oscillation in association withidentifiers specific to each pulse for one cycle's worth; and

output control means, when oscillating one pulse, for reading out asource voltage of a pulse having the same identifier as that one pulsefrom the storage means and effecting the pulse oscillation based on theread-out source voltage.

With such an invention, at the time of oscillation of one pulse duringcontinuous pulse oscillation, source voltage of a pulse having the sameidentifier as that pulse is read from the means for storing and pulseoscillation is effected on the basis of this source voltage. Therefore,in the case where all pulse oscillation for one machined item iscompleted with one cycle of burst mode operation, the read sourcevoltage is data from pulse oscillation at the same position on theprevious machined item; that data has an excitation intensity patterninfluenced by a series of continuous pulse oscillations. In other words,during pulse oscillation, variations of the pulse energy can be morefinely corrected since source voltage having an excitation intensitypattern with the same properties as the previous time is applied.

Therefore, the precision of machining with laser beams can be furtherimproved since the influence of the spiking phenomenon during burst modeoperation can be eliminated as much as possible.

Also, the invention provides a laser apparatus which effects a burstmode operation having as one burst cycle an operation of switching at aprescribed frequency between a continuous oscillation action forcontinuous pulse oscillation of a laser beam at a prescribed frequencyand a stoppage action for stopping the pulse oscillation for aprescribed time, and controls an excitation intensity of the laser insuch a manner that an energy output in the pulse oscillation reaches aprescribed magnitude, characterized in that the apparatus comprises:

storing means for storing a source voltage at a time of each pulseoscillation, in correlation to an oscillation stoppage time, a pulseorder within one burst cycle, and a monitor value of an output pulseenergy, with respect to each of a prescribed number of initial pulseswhen effecting the continuous oscillation action, and storing anexcitation intensity during each pulse oscillation in correlation to amonitor value of the output pulse energy, with respect to each pulsegenerated after the prescribed number of initial pulses;

first source voltage control means which makes a reading of at least oneset of a monitor value of an output pulse energy approaching a targetpulse energy of the current pulse oscillation and an excitationintensity of that pulse, where the oscillation stoppage time and thepulse order within one burst cycle are the same, from among data of pastpulse oscillations stored in the storage means, with respect to each ofthe prescribed number of initial pulses when effecting the continuouspulse oscillation, calculates an excitation intensity during the currentpulse oscillation based on the read value, and effects the pulseoscillation based on the calculated excitation intensity value; and

second source voltage control means which makes a reading of a pulseenergy monitor value of a pulse already output within the current burstperiod and the excitation intensity of that pulse, from the storagemeans, with respect to each pulse generated after the prescribed numberof initial pulses when effecting the continuous pulse oscillation,calculates an excitation intensity during the current pulse oscillationbased on these values, and effects the pulse oscillation based on thecalculated excitation intensity.

Such an invention is constituted so as to effect a type of spike killercontrol in the spike zone including a prescribed number of initialpulses by making a reading of at least one set of a monitor value ofoutput pulse energy approaching target pulse energy of the current pulseoscillation and the excitation intensity of that pulse, whereoscillation stoppage time and pulse order within one burst cycle are thesame, from among stored data of past pulse oscillation stored in themeans for storing; calculating excitation intensity during the currentpulse oscillation based on this read value; and effecting pulseoscillation based on the calculated value of excitation intensity; andso as to effect source voltage control in zones subsequent to the spikezone by reading the pulse energy monitor value of a pulse already outputin the current burst cycle and the value of the excitation intensity atthat time, calculating the excitation intensity value at the time of thecurrent pulse oscillation based on these values, and effecting pulseoscillation based on this excitation intensity.

In other words, the present invention effects spike killer control inthe spike zone, since the influence of the laser oscillation stoppageremains strong, and effects source voltage control (pulse energy controlwithin the burst) according to the situation of the preceding pulseoscillation (output power correlating to impressed source voltage) insubsequent zones, since these are strongly affected by the influence ofpreceding pulses.

Also, the present invention provides a laser apparatus whichcontinuously outputs a prescribed number Nt (NO<Nt) only of pulse laserbeams necessary for machining an object to be machined, for a machiningapparatus to effect machining while an irradiation zone of a pulse laserbeam on the object is displaced by a prescribed pitch each time a pulselaser is irradiated, so that a preset, prescribed number NO of pulselasers are irradiated onto all points on the object, characterized inthat the apparatus comprises:

pulse energy detecting means for detecting a pulse energy Pk (k=1, 2, .. . , Nt) of an output pulse laser beam whenever each pulse laser beamis oscillated; and

target pulse energy revising means, when a set target value of eachpulse laser is Pd and an order of pulse laser beams output continuouslyis i, for calculating a target energy Pt at a time when each of thepulse laser beams is oscillated according to the following formula,changing the calculated target energy Pt to the set target value Pd andoutputting that value, whenever each of the pulse laser beams isoscillated,

in the case where i=1, Pt=Pd

in the case where i≦NO, ##EQU1##

With such an invention, the real exposure from preceding pulse laserbeams is subtracted from the ideal value of exposure at each time and ateach point on the machined object, in the step and scan system, and thisremainder is used as the target value of pulse energy during the currentlaser pulse oscillation.

Furthermore, the present invention provides a laser apparatus whichcontinuously outputs a pulse laser beam for a machining apparatus toeffect a prescribed machining by irradiating a preset, prescribed numberNO of pulse lasers to an object to be machined with an irradiation zoneof the pulse laser beams being fixed, characterized in that theapparatus comprises:

pulse energy detecting means for detecting an energy Pk (k=1, 2, . . . ,No) of an output pulse laser beam whenever each laser beam isoscillated; and

target pulse energy revising means, when a set target value of eachpulse laser is Pd and an order of pulse laser beams output continuouslyis i, for calculating a target energy Pt at a time when each of thepulse laser beams is oscillated according to the following formula,changing the calculated target energy Pt to the set target value Pd andoutputting that value, whenever each of the pulse laser beams isoscillated,

in the case where i=1, Pt=Pd

in the case where i>1, ##EQU2##

With such an invention, the real exposure from preceding pulse laserbeams is subtracted from the ideal value of exposure at each time, inthe stepper system, and this remainder is used as the target value ofpulse energy during the current laser pulse oscillation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram to show the functional constitution of asemiconductor exposure apparatus relating to an embodiment;

FIGS. 2(a) and 2(b) are explanatory diagrams to show the relationshipbetween source voltage V and pulse energy E;

FIG. 3 is a flow chart to show the processing procedures of the outputcontrol portion and control portion in the case of revising pulse energylevel;

FIG. 4 is a diagram to show the arrangement of chips on a wafer;

FIG. 5 is a flow chart to show the processing procedures of the outputcontrol portion in the case of burst mode operation based on thereception interval of the trigger signal Tr;

FIG. 6 is a flow chart to show the processing procedures in the case ofburst mode operation based on the trigger signal for the light machiningcycle;

FIG. 7 is a flow chart to show the processing procedures in the case ofburst mode operation based on the pulse number in a continuous pulsegroup;

FIG. 8 is a flow chart to show the processing procedures in the case ofburst mode operation based on the pulse number in a continuous pulsegroup and a table of only several pulses;

FIG. 9 is a block diagram to show the constitution of another embodimentof the present invention;

FIG. 10 is a time chart of the burst signal and laser oscillationsynchronization signal;

FIG. 11 is a flow chart to show the control procedures of the embodimentin FIG. 9;

FIG. 12 is a flow chart to show the spike control subroutine in FIG. 11;

FIGS. 13(a) and 13(b) are diagrams to show the data read-in subroutineand charging voltage calculation subroutine in the spike controlsubroutine in FIG. 12;

FIGS. 14(a) and 14(b) are diagrams to show another example of the dataread-in subroutine and charging voltage calculation subroutine in thespike control subroutine in FIG. 12;

FIG. 15 is a flow chart to show the control subroutine for burst pulseenergy in FIG. 11;

FIGS. 16(a), 16(b) and 16(c) are flow charts to show the data readsubroutine in the control subroutine for burst pulse energy in FIG. 15;

FIG. 17 is a flow chart to show the charging voltage calculationsubroutine in the control subroutine for burst pulse energy in FIG. 15;

FIGS. 18(a) and 18(b) are diagrams to show experimental results relatingto the charging voltage and pulse energy, in the case where target pulseenergy is changed to three different values and oscillation stoppagetime is changed to two different values in the initial period of burstoscillation;

FIGS. 19(a) and 19(b) are diagrams to show experimental results ofcharging voltage control with the embodiment in FIG. 11;

FIG. 20 is a flow chart to show the control procedures for another modeof the present invention;

FIG. 21 is a flow chart to show the target pulse energy revisionsubroutine in the flow chart in FIG. 20;

FIG. 22 is a diagram to show the irradiation mode of the pulse laserbeam for the IC chip in the step and scan system;

FIG. 23 is a diagram to show the pulse energy waveform in the burstoperation in the case of constant charging voltage;

FIG. 24 is a detail of the pulse energy waveform in FIG. 23 to show thepulse energy wave form of one continuous pulse oscillation;

FIG. 25 is a diagram to show the excitation intensity pattern;

FIG. 26 is an explanatory diagram to show an specific example of thespiking phenomenon; and

FIG. 27 is an explanatory diagram to show a pulse waveform during burstmode operation.

BEST MODE FOR CARRYING OUT THE INVENTION

Below, the laser apparatus relating to the present invention isexplained for the embodiments in the case where the laser apparatus ofthe present invention is applied to a semiconductor exposure apparatususing an excimer laser.

FIG. 1 is a block diagram to show the functional constitution of thesemiconductor exposure apparatus 30 in the present embodiment. As shownin this figure, the semiconductor exposure apparatus 30, generallyspeaking, is constituted of a laser apparatus 1 to output an excimerlaser beam L (below, laser beam L) and an exposure apparatus body 20 toeffect reduction projection exposure with the laser beam L with thislaser apparatus 1 as a light source.

A laser oscillator 22 of the laser apparatus 1 comprises a laser chamberand an optical resonator; the laser chamber is filled with a laser gassuch as Kr and F2 or Ar and F2, Xe and C12, etc. Discharge is effectedbetween electrodes, not pictured, installed above and below the laserchamber, the laser gas is excited, and laser oscillation effected. Theoscillated laser beam resonates within the optical resonator and isoutput as the laser beam L. Moreover, the discharge is effected during aprescribed interval in the prescribed pulse duration; the laser beam Lis output intermittently.

The laser beam L oscillated from the laser oscillator 22 in this way ispartially sampled with a beam splitter 23 and radiated to an outputmonitor 25 a via lens 24. The energy (below, pulse energy) Pi (i=1, 2,3, . . . ) per one pulse of the laser beam L is detected with thisoutput monitor 25. The pulse energy Pi detected with the output monitor25 is sent to an output control portion 26 and is stored in a table asthe pulse energy Pj,i of the i-th in the pulse group No. j as discussedbelow.

The output control portion 26 is connected with a signal line to anexposure apparatus control portion 29 within the exposure apparatus body20. Upon receiving a trigger signal Tr output from the exposureapparatus control portion 29, the output control portion 26 reads thesource voltage stored in the table discussed below and provides thevoltage data based thereon to the laser power source 28. The laser powersource 28 controls the source voltage Vi (i=1, 2, 3, . . . ) accordingto the voltage data given.

Also, the output control portion 26 include s a timer means which is notshown. With this timer means, the output control portion 26 measures insequence the reception time for the trigger signal TR which is sentthereto. Thus, as discussed below, the output control portion 26determines which time corresponds to the laser oscillation stoppage timeaccording to this reception interval time and controls pulseoscillation.

The control portion 27 is the portion to effect calculations necessaryfor the action of the laser apparatus 1. At the time of each pulseoscillation, the detection results Pi from the output monitor 25 aresent to this control portion 27 as well and stored as the pulse energyPrj,i of a pulse which was really oscillated. In other words, thecontrol portion 17 compares the Prj,i with the Pj,i stored in a table ofthe output control portion 16, whenever pulse oscillation is effected.When the difference exceeds the prescribed error range, the controlportion 17 directs the renewal of the source voltage values stored inthe output control portion 26.

Next, the action of the control portion 27 is explained, along with amore detailed explanation of the constitution of the output controlportion 26 discussed above.

The output control portion 26 correlates the source voltage Vj,i ofpulse No. j,i and the value of the pulse energy Pj,i at that time to theparameter j,i (j=1 to N, i=1 to n), which is the identifier of eachpulse, and stores this as characteristic data when all chips on a waferhave been exposed.

Here, the characteristic data are explained. Moreover, this presupposesthe case of effecting burst mode operation as shown in FIG. 27 before.Also, the continuous pulse groups in order are No. 1, No. 2, . . . , No.j, . . . No. N and the pulses within the pulse group No. j in order areNo. j, 1, No. j, 2, . . . , No. j,i, . . . No. j,n.

The relationship between the pulse energy Pj,i and the source voltageVj,i of the initial pulses in the pulse group to suppress the spikingphenomenon differs with respect to the value of the parameter j, even ifthe parameter i is the same, as discussed before. These data are storedin a table and can be rewritten. In the output control portion 26,appropriate data are revised according to directions from the controlportion 27 as discussed below.

As shown in FIG. 27, when burst mode operation is effected, a long laseroscillation stoppage time ΔT is followed again by regular repetition ofalternating between continuous oscillation of a pulse group and a shortoscillation stoppage time. Therefore the Vj,i stored in the table isread, as j and i are the parameters of the pulse to be oscillated, andthis value is supplied to the laser power source 28 as voltage data. Inthis way, the source voltage, having the excitation pattern for chips onthe previous exposed wafer and in the same positions as chips on thewafer to be exposed at the present time, is read and pulse oscillationis effected based on this source voltage. Therefore, the variations ofpulse energy can be more finely corrected tan before, when using thedata for a pulse group for which the preceding laser oscillationstoppage time is the same.

Moreover, in order to find the characteristics of the laser beam inadvance, a trial burst mode operation with the timing shown in FIG. 27is effected initially for the apparatus of the present embodiment. Thesource voltage Vj,i attained at this time and the value of the pulseenergy Pj,i are stored as characteristic data. Moreover, the data fromanother apparatus may be read in and a trial operation not performed.

Meanwhile, concurrent with such control by the output control portion26, real pulse energy Prj,i oscillated from the laser oscillator 22 isinput to the control portion 27 from the output monitor 25 and the valueat that time is compared with the Pj,i, which is stored in the table inthe output control portion 26. When the difference between both exceedsthe prescribed value, the output control portion 26 is instructed torevise the value of Vj,i.

In other words, when the target value of the pulse energy E of one pulseis Ed and the difference between the upper and lower limits of the errorrange, with this value of Ed as the center, is AE, the control portion27 reads Pj,i from the table in the output control portion 26, comparesthis to the Prj,i which was input, determines whether the absolute valueof Pj,i-Prj,i exceeds the following range:

    Ed-ΔE/2≦|Pj,i-Prj,i|≦Ed+ΔE/2

and sends the results of the determination to the output control portion26. The output control portion 26 revises the value of Vj,i in the tableaccording to the results of the determination which were input. In thisway, the pulse energy level can be controlled with good precision over along period of time.

FIGS. 2(a) and 2(b) show the relationship between the source voltage V(2(b)) read from the table and the pulse energy E (2(a)) in the case ofpulse oscillation according to this source voltage V. In this way, pulseoscillation is effected according to the V (j,i) read from the table andthe real pulse energy is monitored; by revising the source voltagevalues stored in the table on this basis, variations in pulse energy Ecan be kept within the desired error range ΔE.

Moreover, Vj,i is revised as follows in the output control portion 26.In other words, in the case where the pulse energy of the laser beamchanges from P to ΔP and when the source voltage is changed from V toV+ΔV during measurement of the laser beam characteristics, this ΔV andΔP are measured, correlated and stored. Since this relationship can beexpressed as the formula ΔV=f (p, ΔP), the degree to which the sourcevoltage may then be revised can be calculated by fitting the increase ordecrease of pulse energy in this formula.

Next, the processing procedures of the output control portion 26 and thecontrol portion 27, in the case of effecting the revision of the pulseenergy level during burst mode operation, is explained with the flowchart in FIG. 3.

The control portion 27 receives input of the actual pulse energy Prj,ifor each single pulse from the output monitor 25 and stores in a memorywhich is not shown (Step 101). Then the control portion 27 reads thePj,i corresponding to the Vj,i of one oscillated pulse from the table inthe output control portion 26 and determines whetherEd-ΔE/2≦|Pj,i-Prj,i|≦Ed+ΔE/2 is established (Step 102). Here, when thisformula is established, the level of pulse energy is within the errorrange and it is not necessary to revise the value of Vj,i; thereforereturns to Step 101 and waits for the oscillation of the next pulse. Onthe other hand, when the formula is not established in Step 102, thelevel of the pulse energy exceeds the error range; therefore, thecontrol portion 27 instructs the output control portion 26 to reviseVj,i (Step 103). In the output control portion 26, the value of Vj,i isrevised according to the relational expression discussed above.

Next, the action of the output control portion 26 during burst modeoperation is explained with exposure of a real wafer as an example.

First, the working procedure during burst mode operation is explained ina simple manner.

FIG. 4 is a model to show the layout of chips on a wafer 21.

For the wafer shown in FIG. 4, the laser beam machining cycle isrepeated as follows: exposure of the laser beam is effected in asideways direction in the order of chips 21-1, 21-2, 21-3 and when 21-5is finished, moves to the next row and effects exposure starting withchip 21-6 in the order of 21-7, 21-8,

The wafer 21 is transported to the exposure position, not pictured,within the exposure apparatus body 29 in FIG. 1 and aligned at aposition where exposure is possible. This time necessary fortransportation and alignment corresponds to the stoppage time ΔT in FIG.27. If alignment is complete, pulse oscillation of a laser beam for thechip 21-1 is started. This pulse oscillation corresponds to the No. 1pulse group in FIG. 27. Then, when the pulse oscillation for the chip21-1 is complete, the optical system is moved, etc. The time necessaryfor this corresponds to the stoppage time ΔT1 in FIG. 27.

Afterwards, the pulse oscillation of the laser beam for the next chip21-2 is started. This pulse oscillation corresponds to the No. 2 pulsegroup in FIG. 27. Then, the same operation is repeated for chips 21-3 .. . 21-5.

When the laser beam oscillation for chip 21-5 is finished, the processmoves to the next row. The time ΔT5 for the optical system to move fromthe chip 21-5 to the chip 21-6 is a longer time than ΔT1 through ΔT4because of the distance and direction of the movement. Afterwards, thesame operation as above is repeated for chips 21-6 to 21-11; when thepulse irradiation for chip 21-11 is complete, the process moves to thenext row. This type of operation is effected for all rows of chips onthe wafer. When exposure is complete, the wafer is transported from theexposure position and the next wafer is transported to the exposureposition and aligned; then the same type of exposure operation isstarted.

Next, the relationship between the burst mode operation and the triggersignal Tr explained in FIG. 1 is explained.

As discussed above, the following various operations are effected withthe exposure apparatus body 29: transport of the wafer, which is themachined object, alignment, movement and positioning of the opticalsystem, wafer transport, and exposure confirmation. At the time whenthis series of operations is finished, an initial trigger signal Tr isoutput to the output control portion 26. The trigger signal Tr at thistime becomes the trigger signal for the radiation of the first pulse inthe No. 1 pulse group in FIG. 27. Then, the trigger signal Tr isrepeatedly output from the exposure apparatus control portion 29 to theoutput control portion (26) until the completion of the exposure of thechip 21-1 shown in FIG. 4; and laser beam irradiation is effected forthe input of each trigger signal. Consequently, the length of the laseroscillation stoppage time ΔTj between the No. j pulse group and the No.j+1 (i=1 to n-1) pulse group can be controlled by the interval at whichthe trigger signal Tr is received. In the same way, the length of th elaser oscillation stoppage time ΔT, necessary for wafer transport,alignment, movement and positioning of the optical system, and wafertransport, can also be controlled by the interval at which the triggersignal Tr is received. Because the laser oscillation stoppage time canbe freely changed in this way, the laser oscillation stoppage time cancorrespond to machining where the laser oscillation stoppage time asshown in FIG. 4 varies while in progress.

Also the timer means, not pictured, with the output control portion 26times the interval at which the trigger signal Tr is received.Therefore, it can be known whether the laser oscillation stoppage timecorresponds to a time in FIG. 27, or whether the continuous pulseoscillation is in progress. In other words, the minimum value Ts and themaximum value Tu of ΔTj (j-1 to n) are determined in advance andcompared with the interval time t at which the trigger signal Tr isreceived. The following determinations are made.

If t<Ts, then the continuous pulse oscillation is in progress

If Ts≦t<Tu, then t=ΔTj (j=1 to n)

If Tu≦t, then t=ΔT

Moreover, all or part of these calculations are actually effected withthe control portion 27, but they are explained below as if effected withthe output control portion 26 in order to make the explanation easy tounderstand.

Next, the processing procedures of the output control portion 26, in thecase of effecting burst mode operation based on the receiving intervalof the trigger signal Tr, are explained with the flow chart in FIG. 5.

The output control portion 26 effects a test operation in burst mode,stores the source voltage Vj,i and pulse energy Pj,i at that time in thetable in correlation to j and i (Step 201), then sets the count number jof the pulse group to 0 (Step 202).

Next, the count number j is increased by one increment (Step 203) andthe count number i of the pulse is set to 0 (Step 204). Then, when thetrigger signal Tr is received from the exposure apparatus controlportion 29 (Step 205), the count number i of the pulse is increased byone increment (Step 206). Then the output controller 26 reads out Vj,istored in the table for the parameters j and i and supplies this valueto the laser power source 8 (Step 207). Moreover, the processing forrevising the table in FIG. 3, discussed above, is effected concurrent toStep 207.

Also, the output control portion 26., concurrent to Step 207, starts thetiming of the time t of the reception interval of the trigger signal Trwith the timer means therein (Step 208). Then, when the output controlportion 26 receives the next trigger signal Tr from the exposureapparatus control portion 29 (Step 209), compares the timed receptioninterval time t with the minimum value Ts, and determines whether t<Ts(Step 210). Here, when t<Ts, in other words when the continuous pulseoscillation is in progress, the output control portion 26 sets t to 0(Step 211) and returns to Step 206. By passing through the loop of Steps206 to 211 in this way, each of the values Vj,i are read from the tablefor all pulses in a single pulse group and supplied to the laser powersource 28.

Meanwhile, when t<Ts is not the case in Step 210, the reception intervaltime t, minimum value Ts, and maximum value Tu are compared and it isdetermined whether Ts≦t<Tu is formed (Step 212). When Ts≦t<Tu is formed,in other words when t is the laser oscillation stoppage time ΔTj betweentwo pulse groups, the output control portion 26 sets t to 0 (Step 213),returns to Step 203, and effects the process for the next pulse group.

When Ts≦t<Tu is not formed in Step 212, in other words when this is thelong laser oscillation stoppage time ΔT for moving the optical system,etc., the output control portion 26 sets t to 0 (Step 214) and returnsto Step 202. In this way, when the processing for a series of continuouspulse groups is complete, returns to Step 202, sets j to 0, and effectsthe processing for the next continuous pulse group.

Such control of the laser oscillation stoppage time is very effective inthe following type of case. In other words, if the energy level of thelaser beam is monitored on the exposure apparatus body 20 as well, itcan be detected if the energy level of each pulse from the laserapparatus 1 varies from the desired value due to variations in thecharacteristics of the optical system between the laser apparatus 1 andthe wafer, for example. In this case, variations in exposure level canbe avoided by adjusting the light energy level of the final pulses in acontinuous pulse group from the exposure apparatus body 20. Moreover,the light energy level of the pulses can be adjusted using a knownvariable optical attenuator. Because this control requires some time,the time to control the variable optical attenuator can be created bydelaying the transmission interval of the trigger signal Tr.

Next, another embodiment, in the case of controlling burst modeoperation with a trigger signal, is explained. In the case where atrigger signal to order one pulse oscillation, a trigger signal to ordercontinuous pulse oscillation, and a trigger signal to order thecompletion of the laser beam machining cycle can be received from theexposure apparatus body 20 in a series of laser beam machining cycles,burst mode operation can be controlled based on these trigger signals.The processing procedure in the case of effecting burst mode operationbased on such trigger signals for the laser beam machining cycle isexplained with the flow chart in FIG. 6.

The output control portion 26 effects a test operation in burst mode,stores the source voltage Vj,i and pulse energy Pj,i at that time in thetable in correlation to j and i (Step 301), then sets the count number jof the pulse group to 0 (Step 302).

Next, the count number j is increased by one increment (Step 303) andthe count number i of the pulse is set to 0 (Step 304). Then, when thetrigger signal Trks for starting the laser beam machining cycle isreceived from the exposure apparatus control portion 29 (Step 305), thecount number i of the pulse is increased by one increment (Step 306).The output control portion 26 reads Vj,i stored in the table for theparameters j and i and supplies this value to the laser power source 28(Step 307). Moreover, the processing for revising the table in FIG. 3,discussed above, is effected concurrent to Step 307.

Next, upon receiving the trigger signal from the exposure apparatuscontrol portion 29, the output control portion 26 determines whetherthat trigger signal is the trigger signal Tr to order the next pulseoscillation (Step 308). Here, when the received signal is the triggersignal Tr, the process returns to Step 306. By passing through the loopof Steps 306 to 308 in this way, each of the values Vj,i are read fromthe table for all pulses in a single pulse group and supplied to thelaser power source 28.

Also, when the trigger signal received in Step 308 is not the triggersignal Tr to order pulse oscillation, the output control portion 26determines whether that trigger signal is the trigger signal TrB toorder the next continuous pulse oscillation (Step 309). When thattrigger signal is the trigger signal TrB to order continuous pulseoscillation, the process returns to Step 303. In this way, when thepulse oscillation in one pulse group is complete, the process returns toStep 303 and effects processing for the next pulse group.

Also, when the trigger signal received in Step 309 is not the triggersignal TrB to order continuous pulse oscillation, the output controlportion 26 determines whether that trigger signal is the trigger signalTrkE for the completion of the laser beam machining cycle (Step 310).When that trigger signal is not the trigger signal TrkE for thecompletion of the laser beam machining cycle, the output control portion26 returns to Step 308 and checks the trigger signal received whilepassing through the loop of Steps 308 to 310. Meanwhile, in Step 310,when that trigger signal is the trigger signal TrkE for the completionof the laser beam machining cycle, the process returns to Step 302. Inthis way, when the processing for a series of continuous pulse groups iscomplete, the output control portion 26 returns to Step 302, sets j to0, and effects processing for the next continuous pulse group.

With the embodiment in FIG. 6, the timing and number of all pulseoscillations in a laser beam machining cycle can be controlledarbitrarily according to each of the trigger signals for a laser beammachining cycle.

Up to this point, processing procedures for effecting burst modeoperation based on the reception interval of the trigger signal Tr (FIG.5) and the trigger signal for the laser beam machining cycle (FIG. 6)have been explained, but burst mode operation can also be controlledwith the pulse number of a continuous pulse group.

Next, the processing procedures in the case of effecting burst modeoperation based on the pulse number of a continuous pulse group isexplained with the flow chart in FIG. 7.

The output control portion 26 effects a test operation in burst mode,stores the source voltage Vj,i and pulse energy Pj,i at that time in thetable in correlation to j and i (Step 401), then sets the count number jof the pulse group to 0 (Step 402).

Next, upon receiving the trigger signal from the exposure apparatuscontrol portion 29 (Step 403), the output control portion 26 increasesthe count number j by one increment (Step 404) and sets the count numberi of the pulse to 0 (Step 405). Then, the output control portion 26reads Vj,i stored in the table for the parameters j and i and suppliesthis value to the laser power source 28 (Step 406). Moreover, theprocessing for revising the table in FIG. 3, discussed above, iseffected concurrent to Step 406.

Next the output control portion 26 increases the count number of thepulse i by one increment (Step 407), compares the count number i of thepulse to the pulse number n, and determines whether i>n (Step 408). Wheni>n is not the case, the process returns to Step 406. By passing throughthe loop of Steps 406 to 408, each of the values Vj,i are read from thetable for all pulses (total number n) in a single pulse group andsupplied to the laser power source 28.

Also, when i>n in Step 408, the output control portion 26 compares thecount number j and total number N of pulse groups and determines whetherj=N (Step 409). When j=N is not the case, the process returns to Step403. In this way, when the processing for all pulse groups is not yetcomplete, the output control portion 26 returns to Step 402 and effectsprocessing for the next pulse group upon receipt of the trigger signalTr.

Also, when j=N in Step 409, in other words when processing for all pulsegroups is complete, the output control portion 26 returns to Step 402,sets j to 0, and effects processing for the next succession of pulsegroups.

In this embodiment, timing of the reception interval time of the triggersignal Tr by the timer means is not necessary, nor is the use ofmultiple trigger signals. In other words, the trigger signal Tr from theexposure apparatus control portion 29 is output only to order theinitial pulse oscillation of a succession of pulse groups. The nexttrigger signal may only be received in the output control portion 26after the predetermined number only of pulse oscillations is repeated.

With the foregoing embodiment, the source voltage Vj,i is read from thetable upon the oscillation of one pulse and supplied to the laser powersource 28. It may also be constituted so that a table for the firstnumber of pulses in a succession of pulse groups is prepared and used tocontrol pulse oscillation, and power lock control, discussed below, iseffected for pulses oscillated after the first number of pulses.

Next, the method for preparing a table only for the first number ofpulses and effecting control is explained as another embodiment.

The constitution of the apparatus in this embodiment is the same as inFIG. 1; the output control portion 26 has the following function.

In the output control portion 26, the pulse energy Pi input from theoutput monitor 25 is stored in a table as the pulse energy Pj,i of thenumber i in the pulse group No. j; the number of pulses Ns at which thespiking phenomenon is markedly exhibited is set in advance and dataregarding pulse characteristics for each pulse group from the start tothe number Ns is stored in the table. When the trigger signal Tr isreceived from the exposure apparatus control portion 29, the sourcevoltage stored in this table is read for the pulses from the start tothe number Ns; voltage data is provided to the laser power source 28based on this. Power lock control (trademark of the Questek company ofthe US) is effected for the pulse oscillated following this number Nspulse. Power lock control is a control to maintain the desired level ofpulse energy Pi, for the phenomenon wherein the laser gas deterioratesand pulse energy Pi drops even through the same source voltage isprovided, by increasing source voltage according to the deterioration ofthe gas. The source voltage for this purpose is called power lockvoltage Vpl.

Also, in this embodiment, the pulse energy Prj,i of a real oscillatedpulse is input to the control portion 27 from the output monitor 25.Each time pulse oscillation is effected, the control portion 27 comparesthe Pj,i stored in the table in the output control portion 26 to thisPrj,i and orders a change to the source voltage value stored in theoutput control portion 26 as necessary.

Next, the processing procedures in the case of effecting burst modeoperation based on the table for only a few pulses discussed above andthe pulse number of the succession of pulse groups is explained with theflow chart in FIG. 8.

The pulse number Ns at which the spiking phenomenon is markedlyexhibited and a set value of source voltage are determined. Then, theoutput control portion 26 effects a test operation in burst mode, storesthe source voltage Vj,i and pulse energy Pj,i at that time in the tablein correlation to j and i (Step 501). However, i is in the range of 1 tons. Next, the output control portion 26 sets the count number j of thepulse group to 0 (Step 502).

Next, upon receiving the trigger signal from the exposure apparatuscontrol portion 29 (Step 503), the output control portion 26 increasesthe count number j by one increment (Step 504) and sets the count numberi of the pulse to 0 (Step 505). Then, the output control portion 26reads Vj,i stored in the table for the parameters j and i and suppliesthis value to the laser power source 28 (Step 506). Moreover, theprocessing for revising the table in FIG. 3, discussed above, iseffected concurrent to Step 506.

Next the output control portion 26 increases the count number of thepulse i by one increment (Step 507), compares the count number i of thepulse to the pulse number Ns, and determines whether i>Ns (Step 508).When i>Ns is not the case, the process returns to Step 506. By passingthrough the loop of Steps 506 to 508, each of the values Vj,i are readfrom the table for the pulses from the start to Ns in a single pulsegroup and supplied to the laser power source 28.

Also, when i>Ns in Step 508, the control moves to power lock control(Step 509).

Next, the output control portion 26 compares the count number i of thepulse and pulse number n and determines whether i>n (Step 510). Here,when i>n is not the case, the process returns to Step 507. By passingthrough the loop of Steps 507 to 510, power lock control is effected forthe remaining pulses (Ns+1 to n) following pulse number Ns.

Also, when i>n in Step 510, the output control portion 26 compares thecount number j and the total number N of pulse groups and determineswhether j=N (Step 511). Here, when j=N is not the case, the processreturns to Step 504. In this way, when processing for all pulse groupsis not yet compete, the output control portion 26 returns to Step 504and effects processing for the next pulse group.

Also, when j=N in Step 511, the process returns to Step 502. In thisway, when processing for all pulse groups is complete, the outputcontrol portion 26 returns to Step 502, sets j to 0, and effectsprocessing for the next succession of pulse groups.

In this way, sufficient practical effects can be attained, even in thecase where the source voltage is read from the table for the initialnumber of pulses and power lock control is effected for subsequentpulses. Also, in such control of laser oscillation stoppage time, it isnot necessary to read the source voltage value from the table for everypulse oscillation; therefore, the processing load on the output controlportion 26 can be reduced. Furthermore, it is possible to economize onmemory capacity since it is not necessary to store data for every pulsein each pulse group.

Moreover, the flow chart in FIG. 8, discussed above, includes branchesto determine pulse number Ns during the process of the flow chart inFIG. 7. However, the method of control using such a table of only anumber of pulses is not limited to the example shown in FIG. 8 and canalso be applied to the flow chart in FIG. 5 or 6, for example.

Next, FIG. 9 shows another constitution in the case where a laserapparatus relating to the present invention is applied as a light sourcein a stepper to effect reduction projection exposure processing ofsemiconductor circuit patterns. Specifically, in FIG. 9, 1 is anarrow-band excimer laser, being a laser apparatus, and 20 is a stepper,being the reduction projection exposure apparatus.

The laser chamber 2 of the excimer laser 1 comprises dischargeelectrodes, etc., not pictured; laser oscillation is effected by theexcitation of the laser gas, comprising Kr, F2, Ne, etc., filling thelaser chamber 2, by the discharge between the discharge electrodes. Thebeam emitted returns to the laser chamber 2 again, amplified,narrow-band with the narrow-banding unit 3, and output as an oscillatedlaser beam L via a front mirror 4. Then, part of the beam returns to thelaser chamber 2 again and laser oscillation occurs. Moreover, the laserbeam L, as shown in FIGS. 23 and 27 before, is output intermittentlywith the burst mode operation which repeatedly alternates between acontinuous oscillation operation, of pulse oscillation continuously at aprescribed frequency for a prescribed period, and a stoppage operation,to stop the continuous pulse oscillation for a prescribed periodfollowing the continuous oscillation operation.

The laser power source circuit 5 provides potential difference V betweenthe discharge electrodes, according to the voltage data provided fromthe laser controller 6, and effects discharge. Moreover, in the laserpower source circuit 5, discharge is effected with the action of aswitch element, such as a thyratron, for example, after being charged upwith the charging circuit, not pictured.

Oscillated from a resonator constituted of a front mirror (4), a laserchamber 2, and a narrow-band unit 3, the laser beam L is partiallysampled with a beam splitter 7 and input to a beam monitor module 8 viaa lens 7a. Also, the remainder of the laser beam L is output to theexposure apparatus 20 via a slit 9.

Each time pulse oscillation is effected, the energy Pi (i=1, 2, 3, . . .) per each pulse of the output laser beam L is detected with the beammonitor module 8. This detected pulse energy value Pi is stored in thetable as the pulse energy Pj,i of the number i in the No. j pulse group.Moreover, the spectral line width and wavelength, etc., of the laserbeam L are detected with the beam output monitor 8, and these data arealso input to the laser controller 6.

The following signals are input to the laser controller 6 from theexposure apparatus 20:

Burst signal BS (See FIG. 10)

Laser oscillation synchronizing signal (external trigger) TR (See FIG.10)

Target pulse energy value Pd

The laser oscillation synchronizing signal TR functions as a triggersignal for each pulse during continuous pulse oscillation with the laserapparatus 1. The burst signal BS functions in such a manner that itsonset starts continuous oscillation operation with the laser apparatus 1(burst on), and its end stops continuous oscillation operation with thelaser apparatus 1 (burst off). The burst signal BS is set so that thefirst laser oscillation synchronizing signal TR is emitted after aprescribed time t1 from burst on, and burst off is effected after aprescribed time t2 following the emission of the final laser oscillationsynchronizing signal TR.

Based on these input signals, the laser controller 6 effects spikecontrol in the spike zone, which includes a prescribed number of initialpulses at the time of continuous pulse oscillation, and effects in-burstpulse energy control in the subsequent plateau and stable zones. Thedetails are explained below.

A beam splitter 11, to sample part of the laser beam L input via a slit10, is installed in the exposure apparatus 20. The sampled light is sentto the beam monitor module 12 via a lens 11a. The energy Pi per onepulse of the input laser beam L is detected in the beam monitor module12. This detected energy Pi is input to the exposure apparatuscontroller (13). Moreover, the laser beam which passed through the beamsplitter 11 is used in reduction exposure processing.

In addition to the control of the movement of the stage on which thewafer is mounted and the reduction exposure processing, the exposureapparatus controller 13 executes the action of transmitting the laseroscillation synchronizing signal TR, burst signal BS, and target pulseenergy value Pd to the laser apparatus 1.

Next, the action of the laser controller 6 during burst mode operationaccording to the flow chart in FIG. 11 is explained.

The laser controller 6 sets the pulse number is of the initial spikezone where spike control should be effected (Step 100). In other words,the pulse number included in the spike zone of FIG. 24 is set as is,since the properties of the pulse energy in continuous pulse oscillationshow properties as shown in FIG. 24, for example.

Next, the laser controller 6 sets the (excitation intensity pattern)charging voltage pattern (initial spike control patter) to be providedduring the initial number is of set pulse oscillations at the time ofthe first continuous pulse oscillation (Step 100).

Next, the laser controller 6 reads in the target pulse energy Pdprovided from the exposure apparatus controller 13 (Step 120) and theninitiates the timing of the oscillation stoppage time (receptioninterval of trigger signal TR) t (Step 130).

Next, when the external trigger signal TR is input from the exposureapparatus controller 13, the laser controller 6 determines whether thisinput external trigger TR is the first external trigger (Step 140). Inother words, since the timer means within, not pictured, times thereception interval Ttr of the trigger signal TR, a comparison of thiselapsed time Ttr to the prescribed set value ts in the laser controller6 can determine whether the current point in time is during thecontinuous oscillation or the stoppage time between the continuousoscillation and the next continuous oscillation.

Specifically, this is the determination: If Ttr<ts, during continuouspulse oscillation If ts≦Ttr, stoppage time between the continuousoscillation and the next continuous oscillation.

Moreover, in this case, since the burst signal BS is input from theexposure apparatus controller 13, the start of the continuousoscillation may be determined by detecting if the burst signal BS is ON.

The laser controller 6 determines that the trigger signal TR input thistime is the first pulse and after setting i=1 (Step 150), determineswhether the current time is the spike zone by comparing this i to thepulse number is of the initial spike zone set previously. In the casewhere it is the spike zone, the laser controller 6 executes the spikecontrol subroutine in Step 180.

FIG. 12 shows the control procedures of the spike control subroutine andeffects the data read-in subroutine (Step 300). In this data read-insubroutine 300, the oscillation stoppage time t, burst pulse number i,target pulse energy Pt are read in and old data relating to the chargingvoltage (excitation intensity) V and the pulse energy P (of the previousburst period) are read with this t, i, and Pt as parameters.

Actually, as shown in FIG. 13 (a) for example, the oscillation stoppagetime t, burst pulse number i, and target pulse energy Pt are read-in(Step 400); data, wherein the burst pulse number i is the same, and theoscillation stoppage time t is the same or closest, is extracted fromold data; and from this extracted data, two items of charging voltagedata and pulse energy data (P1, V1) and (P2, V2) having the pulse energyP closest to the target energy Pt are read (Step 410).

Next, the laser controller 6 executes the charging voltage calculationsubroutine (Step 310) in FIG. 12. In this charging voltage calculationsubroutine, the charging voltage value V to set pulse energy to thetarget value Pt is calculated using the two items of the old data ofcharging voltage data and pulse energy data (P1, V1) and (P2, V2) whichwere read.

Actually, for example, the charging voltage V to realize the targetvalue Pt is calculated using the linear interpolation operation shown inthe following formula and using the two items of old data (P1, V1) and(P2, V2), as shown in FIG. 13 (b) (Step 420).

    (P2-P1)/(V2-V1)=(Pt-P1)/(V-V1)

    V=V1+(V2-V1)(Pt-P1)/(P2-P1)

Next, in FIG. 12, the laser controller 6 outputs the calculatedexcitation intensity value (charging voltage value) V to the powersource apparatus 5 (Step 320) and executes the laser oscillationaccording to this excitation intensity value (charging voltage value) V(Step 330).

When this type of spike control subroutine is compete, the lasercontroller 6 takes the current pulse energy value Pi from the beammonitor module 8 and stores this pulse energy value Pi, along with thecurrent oscillation stoppage time t, burst pulse number i, and thecharging voltage value V actually applied, in the prescribed memorytable (FIG. 11 Step 200). As below, the procedures in Steps 120 to 200are repeated until i=is, specifically until the spike zone is finished.

Next, FIG. 14 (a) shows another example of the data read-in subroutineshown in FIG. 12. Also, FIG. 14 (b) shows another example of thecharging voltage calculation subroutine shown in FIG. 12.

In FIG. 14 (a), the oscillation stoppage time t, burst pulse number i,and target pulse energy Pt are read-in (Step 500); data, wherein theburst pulse number i is the same, and the oscillation stoppage time t isthe same or closest, is extracted from old data; and from this extracteddata, one item of charging voltage data and pulse energy data (P1, V1)having the pulse energy P closest to the target energy Pt is read (Step510).

Also, in the case where such a data read-in subroutine is executed, theone item of old data (P1, V1), which was read, is compared to the targetenergy value Pt (Step 520) in the charging voltage calculationsubroutine as shown in FIG. 14 (b). In the case where P1=Pt, chargingvoltage value V=V1 (Step 530). In the case where Pt>P1, V=V1+ΔV (ΔV:prescribed setting). In the case where Pt<P1, V=V1-ΔV.

When spike control is completed in this way, the laser controller (6)determines the excitation intensity (charging voltage) necessary inorder to set the next pulse energy value to the desired value, from therelationship of the excitation intensity (charging voltage) of the pulseoscillation preceding each pulse and the pulse energy value thereof, inthe plateau zone and stable zone where i>is as shown in FIG. 11 andexecutes the in-burst pulse energy control subroutine to effect pulseoscillation according to the excitation intensity which was determined(Step 190).

In this in-burst pulse energy control subroutine, the data readsubroutine is executed as shown in FIG. 15 (Step 600). In other words,the data read subroutine is the action for reading the pulse energyvalue Pi of a pulse already output in the current burst period and theexcitation intensity (charging voltage) V at that time.

An actual example is shown in FIG. 16 (a) to (c). In FIG. 16 (a), thepulse energy value Pi of the preceding pulse in the current burst periodand the charging voltage V at that time are read (Step 640).

In FIG. 16 (b), the pulse energy value Pi of the pulse preceding the N(for example N=2, N=3, etc.) pulse in the current burst period and thecharging voltage V at that time are read (Step 650).

In FIG. 16 (c), the pulse energy P1 to Pn of n pulses in the currentburst period and the corresponding charging voltage V1 to Vn are readand their average values are set to the pulse energy value P andcharging voltage V for reference (Steps 660, 670).

Moreover, the n pulse which came off the pulse preceding the pertinentpulse may be used as the n pulse shown in FIG. 16 (c).

When this data read subroutine is complete, the laser controller (6)executes the charging voltage calculation subroutine (Step 610) as shownin FIG. 15.

This charging voltage calculation subroutine is for the purpose ofcalculating the charging voltage value V to set the pulse energy to thetarget value Pt using the charging voltage V and the pulse energy Pwhich were read; FIG. 17 shows an actual example.

In other words, the pulse energy value P1 of the read data (P1, V1) iscompared to the target energy value Pt (Step 700) in FIG. 17. In thecase where P1=Pt, charging voltage value V=V1 (Step 710); in the casewhere Pt>P1, V=V1+ΔV (ΔV: prescribed setting); and in the case wherePt<P1, V=V1-ΔV.

When this in-burst pulse energy control subroutine is complete, thelaser controller (6) stores the charging voltage V1 impressed at thistime and its laser output monitor value Pi in the prescribed memorytable (FIG. 1 Step 210). The laser controller (6) repeats suchprocessing until the continuous pulse oscillation of the current burstperiod is complete.

In FIG. 18 shows the results of an experiment under a total of sixdifferent conditions, in the case where the target pulse energy Pd waschanged into three different values P1, P2, and P3 (P1<P2<P3) and theoscillation stoppage time t was changed into two different values ta, tb(ta<tb), in the initial part of burst oscillation. In FIG. 18 (a), themonitor value of each pulse energy is shown for each oscillation orderi. Each charging voltage value Vi for each oscillation order i is shownin FIG. 18 (b).

In this case it is clear that the spiking phenomenon is recovered andeach pulse energy agrees with the target value (P1, P2, P3) as shown inFIG. 18 (a) if the charging voltage shown in FIG. 18 (b) is provided. Asunderstood from FIG. 18 (b), the charging voltage value Vi is greatlyincreased at this time in order to eliminate the spiking phenomenon bythe seventh pulse, but the charging voltage value becomes constant afterthe seventh pulse. Also, since the spiking phenomenon becomes markedwhen the oscillation stoppage time t becomes long, it is understood thatthe charging voltage corresponding to the initial pulse of thecontinuous pulse must be lower when the oscillation stoppage time tbecomes long. Furthermore, it is understood that the charging voltagemust be increased the greater the target pulse energy Pd becomes.

Consequently, in the embodiment shown in FIG. 11, control of theexcitation intensity (charging voltage control) with the target pulseenergy Pd, oscillation stoppage time t, and oscillation order i asparameters, is performed only in the spike zone corresponding to theinitial pulses; in the subsequent plateau zone and stable zone, controlof the excitation intensity (charging voltage control) is performed withreference to the energy value of the pulses already oscillated withinthe current burst period. In other words, spike killer control isperformed in the initial pulses in the continuous pulse oscillationsince the laser oscillation stoppage still has a strong influence. Insubsequent pulses, however, source voltage control according to thecircumstances of the preceding pulse oscillation (output powercorresponding to impressed source voltage) is performed because thepreceding pulse oscillation has greater influence than the laseroscillation stoppage.

FIG. 19 shows the results of an experiment of charging voltage controlwith the embodiment in FIG. 1. All pulse energy values can be to agreeas shown in FIG. 19 (a) through the provision of the charging voltage asshown in FIG. 19 (b).

Next, the control of excitation intensity (charging voltage control)when effecting semiconductor exposure using the step and scan system isexplained with reference to FIGS. 20 to 22.

In other words, as shown in FIG. 4 before, a plurality of IC chips(21-1), (21-1), . . . are arranged on a semiconductor wafer (21); in thestep and scan system, the exposure process is effected while the laserbeam or the wafer (21) is moved. For this reason, in the step and scansystem, the exposure range for one IC chip can be greater, than with astepper to effect exposure processing with a fixed laser beam, and it ispossible to effect exposure processing of a chip with a large area.

Here, with a usual step and scan system, the laser beam irradiation area(area shown with P1, P2, P3 . . . ) is smaller than the area of the ICchip (21) as shown in FIG. 22. These pulse laser beams are scanned at aprescribed pitch ΔP in order and the exposure of the entire surface ofthe IC chip (21) is effected.

In the step and scan system, the scanning pitch ΔP and the irradiationarea of the pulse laser are established so that a predetermined andprescribed number NO of pulse lasers irradiate all points on themachined object. If the pulse energy of each pulse is thereby the sameas the target value Pd, the desired exposure (Pd×NO) can be attained foreach point on the machined object from the irradiation of NO pulse laserbeams.

Actually, the energy of each pulse varies, and it is necessary to dealwith that phenomenon. In this embodiment, that problem is resolved withthe control procedure shown in the flow chart in FIGS. 20 and 21.

For example, in FIG. 22, NO=4 and point A is exposed by the cumulativeenergy of four pulse laser beams P1, P2, P3, and P4; also, point B isexposed by the cumulative energy of four pulse laser beams P2, P3, P4,and P5. The subsequent points C, are exposed by the cumulative energy offour pulse laser beams in the same way.

Consequently, in the step and scan system, it is necessary to controleach pulse energy value so that the shifting cumulative exposure of eachpoint (for example, shifting cumulative exposure of point A isP1+P2+P3+P4) becomes equal.

The control for that purpose is shown in the target pulse energyrevision subroutine of Step 870 in the flow chart in FIG. 20.

Below, the control procedures shown in FIGS. 20 and 21 are explained.

The laser controller (6) sets the pulse number is of the initial spikezone where spike control must be performed (Step 800).

Next, the laser controller (6) sets the charging voltage pattern(initial spike control pattern) to be provided at the time of theinitial is pulse oscillation which was determined at the time of thefirst continuous pulse oscillation (Step 810).

Next, the laser controller (6) reads in the target pulse energy Pdprovided from the exposure apparatus controller (13) and the targetvalue NO of the number of shifting cumulative pulses (Step 820) and thenstarts the timing of the oscillation stoppage time (reception intervalof the trigger signal TR) t (Step 830).

Next, when the external trigger TR is input from the exposure apparatuscontroller (13), the laser controller (6) determines whether thisexternal trigger TR which was input is the first external trigger (Step840).

When the laser controller (6) determines that the trigger signal TRinput this time is the first pulse, the laser controller (6) sets i=1(Step 850) and then executes the revision subroutine for the targetpulse energy (Step 870).

The procedures as shown in FIG. 21 are executed in this target pulseenergy revision subroutine.

In other words, the current i value (this i is the value of the count ofthe total number of oscillations following the start of the pulseoscillation in one continuous pulse oscillation) is compared to thetarget value NO of the number of shifting cumulative pulses (Step 940).In the case where i=1, the target pulse energy Pt following revision isoutput as the target pulse energy Pd which was set previously (Step950). In the case where i≦NO, the target pulse energy Pt followingrevision is calculated according to the following formula (1) (Step960). ##EQU3##

Also, in the case where i>NO, the target pulse energy Pt followingrevision is calculated according to the following formula (2) (Step970). ##EQU4##

Moreover, in these formulas, Pk is the pulse energy value actuallymonitored at the time of each pulse oscillation.

In other words, in the formula (1), the real exposure P1+P2+Pi-1 due tolaser oscillation up to number (i-1) is subtracted from the target value(ideal value ) Pd×i when exposure up to number i was effected, and theremainder is calculated as the target value Pt when effecting number ilaser oscillation; such a revision calculation is executed while i≦NO.

This formula (1) is a formula for a calculation to revise point A inFIG. 22.

The procedure in formula (2) is a formula for a calculation to revisethe target energy in the case where i>NO. This is the formula for acalculation to revise point B and later (point B and points in the zoneto the right of B) in FIG. 22.

When this type of target pulse energy revision subroutine is complete,it is determined whether the current point is in the spike zone (Step880) by comparing i with the pulse number is which was set at the startof the spike zone. In the case where it was determined to be the spikezone, the laser controller (6) executes the spike control subroutine inStep 890.

In this spike control subroutine, action is the same as shown in FIGS.12 to 14 above. Data, wherein the burst pulse number i is the same, andthe oscillation stoppage time t is the same or closest, is extractedfrom old data; and from this extracted data, charging voltage data andpulse energy data having the pulse energy P closest to the target energyPt are read. Using the pulse energy data and charging voltage data whichwere read, charging voltage value V, to set the pulse energy to therevised target value Pt, is calculated and laser oscillation accordingto the calculated charging voltage value is executed.

When this type of spike control subroutine is complete, the lasercontroller (6) takes the current pulse energy value Pi from the beammonitor module (8) and stores this pulse energy value Pi in theprescribed memory table, along with the current oscillation stoppagetime t, burst pulse order i, and the charging voltage value V which wasactually impressed (Step 900). In the same way as below, the proceduresfrom step 820 to Step 900 are repeated until i=is, in other words, untilthe spike zone is finished.

When the spike control is completed in this way, the laser controller(6) executes the in-burst pulse energy control subroutine in the plateauzone and stable zone where i>is (Step 190). In this in-burst pulseenergy control subroutine, the same type of action as in FIGS. 15 to 17above is taken. The pulse energy value Pi of a pulse already output inthe current burst period and the charging voltage at that time are read.Using the charging voltage V and the pulse energy value P which wereread, the charging voltage value V, to set the pulse energy to thetarget value Pt, is calculated and laser oscillation is executedaccording to the calculated charging voltage value.

When this type of in-burst pulse energy control subroutine is complete,the laser controller (6) stores the currently impressed charging voltageVi and the monitor value Pi of that laser output in the prescribedmemory table (Step 920).

In the laser controller (6), this type of processing is repeated untilthe continuous pulse oscillation of the current burst period iscomplete.

Moreover, in the case where the laser apparatus of the present inventionis used as the light source for the exposure apparatus, the controlprocedures in FIGS. 20 and 21 can also be applied in the case where theexposure apparatus is a stepper and not only in the case where it is thestep and scan system.

Specifically, in the stepper system, the target energy Pt whenoscillating each pulse laser beam may be calculated according to thefollowing formula and the calculated target energy Pt may be changed tothe set target value Pd and output, in the case where the number of beampulses to irradiate one IC chip is NO, the target value of each pulselaser beam is Pd, the pulse energy value actually monitored at the timeof each pulse oscillation is Pk (1≦k≦NO), and the order of the pulselaser beams output successively is i.

In the case where i=1,

    Pt=Pd

In the case where i>1, ##EQU5##

With such an embodiment, in the stepper system, the real exposure due tothe preceding pulse laser beams is subtracted from the ideal value ofexposure at each point in time and the result of the subtraction is setto the target value of pulse energy at the time of the current laserpulse oscillation; therefore, the target value of pulse energy for eachpulse oscillation is converted to a value essentially closer to theideal in order to make each pulse energy uniform; and thereby theuniformity of each pulse energy can be contrived. Of course, through theaddition of this revision calculation of the target pulse energy to thecontrol procedure shown in FIG. 1, a revision calculation of targetpulse energy may be effected, along with spike control and in-burstpulse energy control. Thereby, more uniformity of each pulse energy canbe contrived in the stepper system.

INDUSTRIAL APPLICABILITY

As explained above, for each oscillation of one pulse in a succession ofpulse oscillations, source voltage of a pulse having the same identifierof that pulse is read from a storage means and pulse oscillation iseffected based on this source voltage with the present invention.Accordingly, in the case where all pulse oscillation for one machinedobject is completed with one cycle of burst mode operation, the sourcevoltage which is read is data from pulse oscillation at the sameposition on the previous machined object. This data has an excitationintensity pattern influenced by a series of successive pulseoscillations. Specifically, variations of pulse energy during pulseoscillation can be more precisely resolved because of the application ofsource voltage having the excitation intensity pattern with the samecharacteristics as the previous time. Consequently, the precision ofmachining with laser beams can be further improved since the influenceof the spiking phenomenon during burst mode operation can be eliminatedas much as possible.

Also, with the present invention, sufficient suppression of variationsin pulse energy can be attained for all pulses in continuous pulseoscillation and high precision laser beam machining can be realized,because the spike killer control is executed in the spike zone andsource voltage control according to previous pulse oscillationcircumstances is executed in subsequent zones. Furthermore, with thepresent invention, the amount of stored data can be reduced and thememory capacity decreased and moreover, data reading from memory at ahigher speed becomes possible because spike killer control is executedonly in the spike zone.

Also, with the present invention, the exposure at each point on amachined object can be uniform and high precision laser beam machiningcan be realized in a laser beam machining apparatus using the step andscan system, because the real exposure by the preceding pulse laserbeams is subtracted from an ideal value of exposure at each time and theresult of subtraction is made the target value of the pulse energy atthe time of each laser pulse oscillation, in a laser apparatus to outputcontinuously pulse laser beams for a machining apparatus to executemachining while the irradiation zone of a pulse laser on the machinedobject is displaced by a prescribed pitch each time a pulse laser isirradiated, so that a predetermined, prescribed number of pulse lasersirradiate all points on a machined object.

We claim:
 1. A laser apparatus which effects a burst mode operationhaving as one cycle an operation of switching at a prescribed frequencybetween a continuous oscillation action for continuous pulse oscillationof a laser beam at a prescribed frequency and a stoppage action forstopping the pulse oscillation for a prescribed time, and controls asource voltage in such a manner that an energy output in the pulseoscillation reaches a prescribed magnitude, characterized in that theapparatus comprises:storage means for storing the source voltage of eachpulse when effecting the continuous pulse oscillation in associationwith identifiers specific to each pulse for one cycle's worth; andoutput control means, when oscillating one pulse, for reading out asource voltage of a pulse having the same identifier as that one pulsefrom the storage means and effecting the pulse oscillation based on theread-out source voltage.
 2. The laser apparatus according to claim 1,wherein in the storage means, the source voltage and an output energy ofeach pulse of the time when effecting the continuous pulse oscillationare stored for one cycle in association with the identifier specific toeach pulse, and detection of a real output energy of an oscillated pulseis effected whenever one pulse is oscillated, reading of an outputenergy of a pulse having the same identifier of the oscillated pulsefrom the storage means is effected, and revision of a value of thesource voltage having the same identifier as the oscillated pulse iseffected when a difference between both exceeds a prescribed range. 3.The laser apparatus according to claim 1, wherein the laser apparatusreceives a trigger signal for instructing one pulse oscillation, countsa timing a reception interval of the trigger signal, finds the receptioninterval whenever the trigger signal is received; and controls the pulseoscillation in accordance with the reception interval.
 4. The laserapparatus according to claim 1, wherein the laser apparatus receives afirst trigger signal for instructing one pulse oscillation, a secondtrigger signal for instructing the continuous pulse oscillation and athird trigger signal for instructing a completion of one cycle, andcontrols the pulse oscillation in accordance with the received triggersignal.
 5. The laser apparatus according to claim 1, wherein the laserapparatus counts the pulse number of a succession of pulse oscillationsand controls the pulse oscillation in accordance wit h the count number.6. A laser apparatus which effects a burst mode operation having as oneburst cycle an operation of switching at a prescribed frequency betweena continuous oscillation action for continuous pulse oscillation of alaser beam at a prescribed frequency and a stoppage action for stoppingthe pulse oscillation for a prescribed time, and controls an excitationintensity of the laser in such a manner that an energy output in thepulse oscillation reaches a prescribed magnitude, characterized in thatthe apparatus comprises:storing means for storing a source voltage at atime of each pulse oscillation, in correlation to an oscillationstoppage time, a pulse order within one burst cycle, and a monitor valueof an output pulse energy, with respect to each of a prescribed numberof initial pulses when effecting the continuous oscillation action, andstoring an excitation intensity during each pulse oscillation incorrelation to a monitor value of the output pulse energy, with respectto each pulse generated after the prescribed number of initial pulses;first source voltage control means which makes a reading of at least oneset of a monitor value of an output pulse energy approaching a targetpulse energy of the current pulse oscillation and an excitationintensity of that pulse, where the oscillation stoppage time and thepulse order within one burst cycle are the same, from among data of pastpulse oscillations stored in the storage means, with respect to each ofthe prescribed number of initial pulses when effecting the continuouspulse oscillation, calculates an excitation intensity during the currentpulse oscillation based on the read value, and effects the pulseoscillation based on the calculated excitation intensity value; andsecond source voltage control means which makes a reading of a pulseenergy monitor value of a pulse already output within the current burstperiod and the excitation intensity of that pulse, from the storagemeans, with respect to each pulse generated after the prescribed numberof initial pulses when effecting the continuous pulse oscillation,calculates an excitation intensity during the current pulse oscillationbased on these values, and effects the pulse oscillation based on thecalculated excitation intensity.
 7. The laser apparatus according toclaim 6, wherein the first source voltage control means reads out twosets of a monitor value of an output pulse energy closest to the targetpulse energy of the current pulse oscillation and an excitationintensity at that time, and calculates the excitation intensity value atthe time of the current pulse oscillation with an interpolationcalculation using the two sets of excitation intensity values.
 8. Thelaser apparatus according to claim 6, wherein the first source voltagecontrol means reads out one set of a monitor value of an output pulseenergy closest to the target pulse energy of the current pulseoscillation and an excitation intensity at that time, and calculates theexcitation intensity value at the time of the current pulse oscillationby changing the read-out excitation intensity according to a result ofcomparing the target pulse energy value and a monitor value of theread-out output pulse energy.
 9. A laser apparatus which continuouslyoutputs a prescribed number Nt (NO<Nt) only of pulse laser beamsnecessary for machining an object to be machined, for a machiningapparatus to effect machining while an irradiation zone of a pulse laserbeam on the object is displaced by a prescribed pitch each time a pulselaser is irradiated, so that a preset, prescribed number NO of pulselasers are irradiated onto all points on the object, characterized inthat the apparatus comprises:pulse energy detecting means for detectinga pulse energy Pk (k=1, 2, . . . , Nt) of an output pulse laser beamwhenever each pulse laser beam is oscillated; and target pulse energyrevising means, when a set target value of each pulse laser is Pd and anorder of pulse laser beams output continuously is i, for calculating atarget energy Pt at a time when each of the pulse laser beams isoscillated according to the following formula, changing the calculatedtarget energy Pt to the set target value Pd and outputting that value,whenever each of the pulse laser beams is oscillated, in the case wherei=1, Pt=Pd in the case where i≦NO, ##EQU6## in the case where i>NO##EQU7##10.
 10. A laser apparatus which continuously outputs a pulselaser beam for a machining apparatus to effect a prescribed machining byirradiating a preset, prescribed number NO of pulse lasers to an objectto be machined with an irradiation zone of the pulse laser beams beingfixed, characterized in that the apparatus comprises: pulse energydetecting means for detecting an energy Pk (k=1, 2, . . . , No) of anoutput pulse laser beam whenever each laser beam is oscillated;andtarget pulse energy revising means, when a set target value of eachpulse laser is Pd and an order of pulse laser beams output continuouslyis i, for calculating a target energy Pt at a time when each of thepulse laser beams is oscillated according to the following formula,changing the calculated target energy Pt to the set target value Pd andoutputting that value, whenever each of the pulse laser beams isoscillated, in the case where i=1, Pt=Pd in the case where i>1, ##EQU8##